1. Field of the Invention
The invention relates to methods and systems for imparting desired shape and surface characteristics to a moldable or pliable material as the material cures or hardens. It is particularly applicable to the shaping and embossing of thermosetting resin systems during curing, and can be used to form these resin systems into a variety of products, including synthetic lumber, roofing, and siding.
2. Description of Related Art
Various techniques exist for continuously forming a soft or moldable material while it hardens or cures. For example, conveyor belts can be used to provide continuous support and movement for materials, and in some cases the belt faces may be contoured or profiled to mold the surfaces of the material and to impart a shape, feature, or surface appearance to the material. Two or more such belts may be configured to operate with the belt surfaces opposed and the material to be molded or shaped disposed between them. These systems can form fairly detailed three-dimensional products.
However, when such systems are used to form a foamed product, the structure of the overall system must be sufficiently strong to contain the pressure of the expanding foam. The longer the forming system and the larger the cross-section of the product to be formed, the greater the total force due to pressure and friction that the system must contain and overcome. As a result, in general, belt systems have not been thought to be suitable for formation of resin systems that involve foaming of the polymer matrix.
Forming systems have been developed to produce large rectangular polyurethane foam buns; these systems typically contain the foaming material within roller-supported films or sheets. The many rollers used in these systems contain the increase in pressure due to foaming, and also help to minimize system friction. However, these systems are generally not able to mold detail or texture into the product surface.
Pullers are two-belted machines designed to grip and pull an extruded profile. As indicated above, conventional two-belt systems, such as pullers that utilize thick profiled belts, may be configured to continuously mold detail and texture into a product. However, these forming systems typically require profiled belts with relatively thick sidewall cross sections. The thick sidewalls minimize deflection of the unsupported sides of the mold-belt, thereby maintaining the intended product shape, and limiting extrusion of material through the resultant gap between belts. The thickness of the product formed by a conventional two-belt system is thus limited in practice by the thickness and width of the profiled mold-belts. Thicker belts needed to form products with deeper profiles require larger diameter end pulleys in order to prevent excessive bending, stretching, and premature breakage of the mold material.
In addition, most pullers are relatively short (6 feet or less). These short forming systems tend to require slower production speeds, allowing the product enough time in-mold to harden sufficiently before exiting the forming unit. Longer two-belt machines can be made, but in order to manage belt/bed friction these longer systems typically require the use of rollers to support the back of the profiled belts. Roller supported mold-belts tend to allow the mold faces to separate between rollers where the belts are unsupported, allowing material to leak between belt faces.
To continuously mold larger foamed cross-sections and to impart irregular shape or surface detail to the product, table-top conveyors are frequently used. Table-top conveyors use segmented metal mold sections attached to a metal chain-type conveyor. Two table-top conveyors are typically arranged face-to-face when used in this type of application, providing a rigid continuous mold. Preventing material from migrating into the joints between adjacent mold sections can be problematic for this type of forming system and may required the use of plastic films disposed between the mold and material to prevent leaks. In addition, such table-top conveyor systems are complex and costly.
Because of the various difficulties and deficiencies described above for existing forming systems, there remains a need in the art for a low cost forming system that can shape a curing polymer system, and in particular a foaming polymer system, without leaking. There is a need for such a system that can impart surface patterns and designs to the curing material, and that has sufficiently low friction and thickness that it can be practically made long enough to allow sufficient curing time in the system.